3/4 inch supply line to master bath, but 1/2 inch line at shower valve?

We have 3/4 supply lines coming into the master bathroom (sink and shower) and about 5 feet of 1/2 inch to the bathtub. We are doing a complete remodel and the bathtub 1/2 line is closest to the new shower location. We are installing a Kohler Water tile Rain Head, 3 body sprays and hand shower.

So what makes more sense.

1. Use the 1/2 inch line with a 1/2 inch valve
2. Use the 1/2 inch line, but with a 3/4 inch valve
2. Cap off the 1/2 inch line and reroute one of the 3/4 supply lines to the valve?

The system would never have more then 2 devices running at the same time, plus we have a 60 gallon water heater. So we don't want a 5 minute shower either.

What kinda volume are we looking at per body spray??? The handheld and the rainhead are suppose to be limited to 2.5 gal per minute at 80 psi I believe. We need to calculate how much water you will be needing with two functions in use.
Most 1/2" shower valves will run over 7 or 8 gallons a minute.

Check the specs on the 1/2 valve and see what it will flow with the 60 psi you have compared to the total of the gallons your two functions will use.

It depends on how many of those things you want to run at once! Unless your hot water supply is hotter than normally allowed (that's 120-degrees), you'll be using mostly hot water, especially in winter when the incoming supply water is (often) much colder, a 1/2" valve would be hard pressed to deliver those specs within the safe flow velocity of the water pipes (about 5pfs). Faster water flow creates turbulence, noise, and can literally create holes in the piping after time.

You need to look at the specs of the individual sprays you want to run at once. Add them up. Four body sprays by themselves could run anywhere from 2-10gpm depending on their design. Then, add one other showerhead, and you've overloaded the system, and the performance will be lousy.

The Kohler body sprays are 2.5 gpm, we're installing either 2 or 3. We would only have them going with one other device at the same time.

Since all the main lines are 3/4 to the bathroom, do you think 4-5 feet of 1/2 would hurt the pressure that much? If we bumped the 1/2 inch line back to 3/4 before the valve?

We can reroute another 3/4, but it would take time and be a little tricky. But doable

Thanks for all the info guys!

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Running 3 body sprays plus another function would put you at 10 gpm. If you had a hot water temp setting of 120 degrees and a cold incoming water temp of 60 degrees and a mixed shower temp of 105 degrees you would be using 75% hot water.

You would get about 5 minute shower at 105 degrees running 10 gpm. assuming the water heater had its full capacity of storage at the time you wanted a shower.

If you had a hot water temp of 140 degrees and a incoming water temp of 60 degrees with a shower temp of 105 degrees you would be using 56% hot water to achieve that ratio. Your shower would last roughly 20% longer......thats not much.

You stated you have a 60 gal heater.

I can already tell you your water heater is undersized for what you have planned.

For 3 bodysprays running 2.5 gpm each and another function of 2.5 gpm I would use the 3/4 valve and run 3/4 piping to it for sure. If you did 2 body sprays plus another function totaling 7.5 gpm I would use the 1/2 thermostatic. and leave the piping alone.

Consider installing two 50 gal water heaters in parallel set at 140 degrees with a tempering valve set at 125. Fly me over to Texas to supervise the job. LOL

The bodysprays are rated usually at 80 psi. Kohler doesn't list the pressure but lists the volume at 2.5 gpm. If you have 60 psi at the meter you will have some pressure loss by the time you get the water to the bodysprays because of friction through the pipe,fittings and valves.

You would get 75% of the listed volume with 60 psi, That calculates out to 1.875 gpm. Multiply times 3 for the bodysprays and you get 5.625 gpm. Now figure in a little pressure loss and you would at best be getting 5 gpm out of all 3 bodysprays. Now add another 1.875 for the second function minus some pressure loss through the piping and you would get about 1.5 gpm. Total your going to be running about 6 to 7 gpm.

Thats unless you remove flow restrictors.......thats illegal tho. No one really does that do they??? LOL

As a practical matter, if you compute the actual size of the openings in a 3/4 valve, you will find that a 1/2" a pipe has the same, or almost the same, area, so you can use any of your options and have the same results.

Just checked with the city, and our PSI averages between 65 to 85. Since we live right by a pump station and a ground level water tower, they think it's pretty high. They're sending somebody by this afternoon or in the morning, to measure it.

Would that matter, if I have 80 PSI? If we went with the 1/2 valve? Any benefits of piping the 1/2 into a 3/4 valve?

FWIW, industry says that 5-6fps flow velocity is about the fastest you can run water through a 1/2" supply line without having long-term problems. That amounts to under 4gpm for a single 1/2" supply line. Since you have both hot and cold, a max might be around 8gpm. Short sections of narrower restrictions cause the water to speed up (venture effect) to compensate, and the flow rate doesn't change much unless there are a lot of them, or they're longer. How a 1/2" valve can claim over 10gpm is not very realistic..I'd like to see their test results. You might be able to do that if your pressure was excessive, but the flow velocity would be beyond maximum for industry standards...it's not like they can reinvent the rules here.

Most reliable, realistic 1/2" shower/tub valves are rated 6-7gpm. And, you'll only achieve that when your water is using almost a 50-50 mix of hot and cold which is unrealistic, especially in the winter. When your mix ends up more like 80-20 hot/cold in the winter, the max flow rate goes down.

A 1/2" valve is typically only good for two heads max, and depending on your supply lines (pex or cpvc would be pushing even that) and pressure, may not provide great results even with that.

As is discussed a lot here, if you have the vertical height to install one, a waste water heat recovery system could extend your shower with the same WH at a significant energy savings verses a bigger WH, and lengthen the available shower time. A little searching will show you some of this info.

FWIW, industry says that 5-6fps flow velocity is about the fastest you can run water through a 1/2" supply line without having long-term problems. That amounts to under 4gpm for a single 1/2" supply line. Since you have both hot and cold, a max might be around 8gpm. Short sections of narrower restrictions cause the water to speed up (venture effect) to compensate, and the flow rate doesn't change much unless there are a lot of them, or they're longer. How a 1/2" valve can claim over 10gpm is not very realistic..I'd like to see their test results. You might be able to do that if your pressure was excessive, but the flow velocity would be beyond maximum for industry standards...it's not like they can reinvent the rules here.

Most reliable, realistic 1/2" shower/tub valves are rated 6-7gpm. And, you'll only achieve that when your water is using almost a 50-50 mix of hot and cold which is unrealistic, especially in the winter. When your mix ends up more like 80-20 hot/cold in the winter, the max flow rate goes down.

A 1/2" valve is typically only good for two heads max, and depending on your supply lines (pex or cpvc would be pushing even that) and pressure, may not provide great results even with that.

As is discussed a lot here, if you have the vertical height to install one, a waste water heat recovery system could extend your shower with the same WH at a significant energy savings verses a bigger WH, and lengthen the available shower time. A little searching will show you some of this info.

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Your using the 5gpm in the wrong way. Intermittent use is fine to exceed the 5gpm. Hose Bibbs often exceeds the 5gpm limit without ill effects because its not ran all day everyday.

Delta faucet co rough valve will accept several different cartridges. If you use the T17253 cartridge you will get about 6.8 GPM.......if you use the T17T253 cartridge you get about 9GPM. The valve has 1/2" inlets and outlets. Check for yurself. Its within their frequently asked questions of custom showers.

Copper and pex is sized the same way.......pex makes up for the insert fittings by using less fittings in the system. The walls of pex do not build scale like copper either.

The internet and books usually do not tell the whole story. After about 30 years you tend to know fact from fiction.

Thats a Delta system that runs two different functions at once in any combination. The bodysprays run 2.0 gpm @80 psi. The owner loves it and it soaks you.

Hey Guys, thanks again for all the info. We did finalize the plumbing this afternoon. We're going with the 3/4 to the valve.

In the end, we're talking about 2 hours of work, to reroute the 3/4 to the shower. From what I read on this site, it's best to have too much then too little. We will install volume control valves on each device, to regulate the water flow so we don't end up with a 3 minute shower! LOL